The founders did not want any one branch of government to overpower the others. For example, the President can appoint judges to the Supreme Court, but the Congress has to approve them and once judges are appointed, they are appointed for life. The idea is that if a president doesn't like the way the court is going, he can appoint a judge whose views he agrees with, but only when an opening comes up.

You've got lots of good information in previous posts. The purpose behind the separation of powers was to prevent any one branch of the government from becoming all-powerful by limiting the functions that could be carried out by one branch - the judicial branch has no power to raise funds to pay for governmental activity, the executive branch cannot introduce legislation into Congress, the legislative branch cannot enter into treaties with foreign governments. Checks and balances were another safeguard, created to allow each branch of government means to counteract actions that were beyond the appropriate scope of its powers.

I think something often overlooked in the United States government and the checks and balances provided for by the founding fathers is the people. The final check and balance is the American public who can vote individuals into or out of political positions, I think that the last round of elections begin to show this as more incumbents were voted out of office as a sign that they were not doing what the people who elected them wanted.

Checks and balances and the separation of powers are vital mechanisms to ensure the smooth running of democracy. Checks and balances operate to ensure that no one body or group of people ever are able to have so much power that they are able to disproportianately influence the legal system or law making of a country. Ensuring that any new law has to go through a system of intense scrutiny, for example, is one way of helping to ensure the long and successful life of democracy.

The basic concept is that no one part of government (much less one person) should be able to make policy easily. Every person or part of government should only have a limited amount of power (separation of powers) and should have other people/parts of government that can block their actions (checks and balances). This is a major founding principle of our country -- that no part of government should have the ability to wield uncontrolled power. The idea was to make it much harder for government to tyrannize the people.